The present invention relates to nuclear power reactor fuel bundles and, in particular, to an improved apparatus for the assembly and disassembly the upper tie plate of such bundles.
In a typical nuclear power reactor, nuclear fission occurs within fuel rods which are assembled into bundles with the fuel rods in a parallel array between two tie plates. A multiplicity of fuel rods constitute the fuel core of a reactor. Heat from the nuclear fission reaction is taken up by a fluid (usually water) flowing along the outer surface of the rods. As the reactor operates, the fuel is gradually consumed, and it is necessary at periodic intervals to replace the fuel. However, only a minor fraction of the fuel rods are replaced at any one time, in order to avoid large variations in reactor operation. In the event of premature bundle failure or fuel inspection, it is necessary to remove the bundles and to disassemble them for repairs, replacement, or inspection of selected rods. Thus, the fundles may be adapted for easy disassembly by remote means, since they become highly radioactive during the operation of the reactor. Disassembly requires the removal of the upper tie plate in order to reach the fuel rods.
A number of arrangements have been disclosed in the prior art for assembling nuclear power reactor fuel bundles. See for example, U.S. Pat. Nos. 3,431,170 and 3,953,287, the latter being assigned to the same assignee as the present application. Many of the prior art arrangements, however, require the removal of relatively small parts to remove the upper tie plate which is difficult to do by remote disassembly techniques. Any system for locking fuel rods in a fuel bundle should be as simple as possible, not only to reduce the cost of the locking system employed, but also to simplify the complicated procedures for the subsequent disassembly and reassembly of the bundles under remote control conditions. The possibility of losing parts during remote disassembly make it highly desirable to provide a locking system which, preferably, need not be disassembled at any time after the initial assembly.
The structure of U.S. Pat. No. 3,953,287 avoids this difficulty, but it, as well as that of the other patent, is only applicable to fuel assemblies in which the upper tie plate is loaded by springs which push it upwardly. There is need for a design which is readily operable remotely, which avoids separable parts and which is applicable to fuel assemblies in which the upper tie plate is rigidly mounted on the tie rods which hold it in place.
U.S. Pat. No. 3,971,575 shows another arrangement for a locking device that combines a number of the parts of the locking system on one assembly.